ROS与Opencv基础篇_ros opencv

#!/usr/bin/env python
# -*- coding: utf-8 -*-
 
import rospy
import cv2
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image
 
class image_converter:
    def __init__(self):    
        # 创建cv_bridge，声明图像的发布者和订阅者
        self.image_pub = rospy.Publisher("cv_bridge_image", Image, queue_size=1)
        self.bridge = CvBridge()
        self.image_sub = rospy.Subscriber("/usb_cam/image_raw", Image, self.callback)
 
    def callback(self,data):
        # 使用cv_bridge将ROS的图像数据转换成OpenCV的图像格式
        try:
            cv_image = self.bridge.imgmsg_to_cv2(data, "bgr8")
        except CvBridgeError as e:
            print (e)
 
        # 在opencv的显示窗口中绘制一个圆，作为标记
        (rows,cols,channels) = cv_image.shape
        if cols > 60 and rows > 60 :
            cv2.circle(cv_image, (60, 60), 30, (0,0,255), -1)
 
        # 显示Opencv格式的图像
        cv2.imshow("Image window", cv_image)
        cv2.waitKey(3)
 
        # 再将opencv格式额数据转换成ros image格式的数据发布
        try:
            self.image_pub.publish(self.bridge.cv2_to_imgmsg(cv_image, "bgr8"))
        except CvBridgeError as e:
            print (e)
 
if __name__ == '__main__':
    try:
        # 初始化ros节点
        rospy.init_node("cv_bridge_test")
        rospy.loginfo("Starting cv_bridge_test node")
        image_converter()
        rospy.spin()
    except KeyboardInterrupt:
        print ("Shutting down cv_bridge_test node.")
        cv2.destroyAllWindows()

分析以上例程代码的关键部分：

import cv2
from cv_bridge import CvBridge, CvBridgeError

要调用Opencv，必须先导入Opencv模块，另外还应导入cv_bridge所需的一些模块

self.image_pub = rospy.Publisher("cv_bridge_image", Image, queue_size=1)
self.bridge = CvBridge()
self.image_sub = rospy.Subscriber("/usb_cam/image_raw", Image, self.callback)

定义一个Subscriber接收原始的图像消息，再定义一个Publisher发布Opencv处理后的图像消息还要定义一个句柄，便于调用相关的转换接口

 try:
            cv_image = self.bridge.imgmsg_to_cv2(data, "bgr8")
        except CvBridgeError as e:
            print (e)

try:
            self.image_pub.publish(self.bridge.cv2_to_imgmsg(cv_image, "bgr8"))
        except CvBridgeError as e:
            print (e)

cv2_to_imgmsg()接口的功能是将opencv格式的图像数据转换成ROS图像消息，该接口要求输入图像数据流和数据格式两个参数